In 16 states and counting, drugs now kill more people than auto accidents do, the government said Wednesday.

Experts said the startling shift reflects two opposite trends: Driving is becoming safer, and the legal and illegal use of powerful prescription painkillers is on the rise.

For decades, traffic accidents have been the biggest cause of injury-related death in the U.S., and they are still No. 1. But drug overdoses are pulling ahead in one state after another.

The drug-related death rate roughly doubled from the late 1990s to 2006, according to the most recent CDC data.

The number of states in which drug-related deaths have overtaken traffic fatalities has gone from eight in 2003 to 12 in 2005, and 16 in 2006. They are: Massachusetts, New Hampshire, Rhode Island, Connecticut, New York, New Jersey, Maryland, Pennsylvania, Ohio, Michigan, Illinois, Colorado, Utah, Nevada, Oregon and Washington.

While cocaine and heroin continue to be significant killers, most of the increase is attributed to prescription opiates such as the painkillers methadone, Oxycontin and Vicodin.

From 1999 to 2006, death rates for such medications climbed for every age group. Deaths from methadone (from msnbc.com) alone increased sevenfold, according to the CDC.

It's not all black market stuff, either.

About half of the opiate medication deaths in King County, Wash., which includes Seattle, involved people who got their drugs through legal prescriptions, said Caleb Banta-Green, a University of Washington research scientist.

"There has been a dramatic change in how doctors prescribe opiates," Banta-Green said.

In the 1990s, he said, doctors began recognizing that chronic pain was undertreated. The prescribing of painkillers escalated after that. Today, about one in five U.S. adults and one in 10 adolescents are prescribed an opiate each year, he said.

Using death certificate data, CDC researchers counted more than 45,000 U.S. deaths nationwide from traffic accidents in 2006, and about 39,000 from drug-induced causes.

About 90 percent of those drug fatalities are sudden deaths from overdoses, but the count includes people who died from organ damage from long-term drug use or abuse.

In Massachusetts, there were more than 1,000 drug-related deaths in 2006, double the number of traffic deaths, according to the CDC. Michigan had about 500 more drug deaths than vehicle fatalities, and New York had 350 more.

Nationally, the death rate from traffic accidents fell by about 6.5 percent from 1999 through 2006 - from 15.3 deaths per 100,000 people to 14.3 per 100,000, according to the National Highway Traffic Safety Administration.